A fogging problem with sport goggle lenses has existed for many years. In snow ski goggles this effect occurs when the interior surface of the lens reaches the dew point. Problems are caused by a combination of cooling of the lens due to contact with cold air, and the flow of moisture into the goggle interior air volume from the face. Air is drawn into the lens-face volume. The air is heated by contact with the face, air filters, and the lens, and causes a drop in relative humidity. The air absorbs water vapor and can flow out of the lens-face volume. If there is sufficient airflow through the goggles, then the lenses can be kept clear of condensing water vapor.
The previous standard, ASTM standard F 659-98, used a water bath heated to 50° C., a circulation fan, and placed the goggle lens between the humidified air and the room air. The previous standard test was designed to test lens coatings and quantified the anti-fogging properties by the time optical obscuration occurred. This test did not address airflow conditions of a goggle when worn on a human face, or steady operation conditions.